中文摘要：

基于中间主应力对岩石强度影响,统一强度理论可作为Coulomb准则的推广,并已得到广泛的研究和使用。利用已有的8种岩石真三轴试验结果,研究强度准则参数的确定方法以及相应的拟合误差。依据常规三轴压缩强度与围压的关系确定Q和K,再依据真三轴的强度确定参数b,统一强度理论所给出的双折线难以描述强度变化的整体趋势,对部分岩石试验数据的拟合误差超过Coulomb准则;如果以最小拟合误差为目标,对参数Q,K和b进行协同搜索,那么统一强度理论可以有较小的拟合误差,但其给出的部分岩石常规三轴压缩强度明显偏离实际结果。此外,统一强度理论认为岩石三轴伸长强度与常规三轴压缩强度相同,在最小主应力恒定时中间主应力引起的强度最大增加值随最小主应力线性增加,且强度关于中间主应力的一阶导数在峰值点是不连续的,这些都与试验结果不能完全协调。由于真三轴压缩试验结果还较少,中间主应力的试验范围也较小,而数据的离散性又较大,以最小拟合误差确定的强度准则能否适用于实际工程的分析计算,需要更深入的研究。

英文摘要：

Unified strength theory is the development of Coulomb criterion with analyzing the effect of intermediate principal stress. It deems that rock has the same strength under conventional triaxial compression and tension; and a zigzag is used to describe the effect of intermediate principal stress on strength. The theory has been studied deeply and used widely. The true triaxial strengths of eight rock samples using the theory are fitted; and the processes of parameters determination and misfits of the fitting solutions are also given. If the parameters of Q and K are determined from the relationship between pseudo-triaxial strength and confining pressure, and only parameter b is determined from true triaxial strengths, the theory can not describe main characteristics of the influence of intermediate principal stress on strength. The misfits for several rock samples may be higher than those from Coulomb criterion. If the parameters of Q, K and b are determined on the least misfit to the whole set of strengths, the theory has a pretty fitness. However, the pseudo-triaxial strengths of several rocks from the best fitting solutions have great scatterness from the real magnitudes. Also, it does not correspond to the experimental results that rock has the same strength under conventional triaxial compression and tension： the maximum increase of strength from intermediate principal stress has a linear relation with the minor principal stress： and the first-order derivative of strength has an interruption at the peak point. Insufficiency of experimental results and dispersion within test data make great difficulty in reviewing the feasibility of the best fitting solutions.